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    Validate Access Tokens

    Info: This topic was archived on February 9 2024 and is no longer updated. PHP is no longer a supported language at Okta.

    This guide explains how to verify a token's signature, manage key rotation, and how to use a refresh token to get a new access token.

    Learning outcomes

    Validate access tokens.

    About access token validation

    If you are building a modern app or API, you likely want to know if your end user is authenticated. This is important to give context or to protect APIs from unauthenticated users. You can use Okta to authenticate your end users and issue them signed access and ID tokens, which your application can then use. It is important that your application only uses the access token to grant access, and not the ID token. For more information about this, see the Access Tokens vs ID Tokens section below.

    After the signed tokens are issued to the end users, they can be passed to your application for validation. There are two ways to verify a token: locally or remotely with Okta. The token is signed with a JSON Web Key (JWK) using the RS256 algorithm. To validate the signature, Okta provides your application with a public key that can be used.

    Access Tokens vs ID Tokens

    As mentioned above, it is important that the resource server (your server-side application) accepts only the access token from a client. This is because access tokens are intended for authorizing access to a resource.

    ID Tokens, on the other hand, are intended for authentication. They provide information about the resource owner, to allow you verify that they are who they say they are. Authentication is the concern of the clients. Because of this, when a client makes an authentication request, the ID Token that is returned contains the client_id in the ID Token's aud claim.

    What to Check When Validating an Access Token

    The high-level overview of validating an access token looks like this:

    • Retrieve and parse your Okta JSON Web Keys (JWK), which should be checked periodically and cached by your application.
    • Decode the access token, which is in JSON Web Token format
    • Verify the signature used to sign the access token
    • Verify the claims found inside the access token

    Retrieve The JSON Web Keys

    The JSON Web Keys (JWK) need to be retrieved from your Okta authorization server, though your application should have them cached. See Best practices. Specifically, your authorization server's Metadata endpoint contains the jwks_uri, which you can use to get the JWK.

    For more information about retrieving this metadata, see Retrieve Authorization Server Metadata.

    Decoding and Validating the Access Token

    You will have to decode the access token, which is in JWT format. This involves the following steps:

    • Verify the Token Signature
    • Verify the Claims

    See the instructions for the Okta JWT Verifier for PHP (opens new window).

    Required Packages

    The Okta JWT Verifier can be installed through composer.

    composer require okta/jwt-verifier

    This library requires a JWT library. We currently support firebase/php-jwt. You will have to install this or create your own adaptor.

    composer require firebase/php-jwt

    You will also need to install a PSR-7 compliant library. We suggest that you use guzzlehttp/psr7 in your project.

    composer require guzzlehttp/psr7

    Validate Access Token

    For any access token to be valid, the following are asserted:

    • Signature is valid (the token was signed by a private key which has a corresponding public key in the JWKS response from the authorization server).
    • Access token is not expired (requires local system time to be in sync with Okta, checks the exp claim of the access token).
    • The aud claim in the jwt matches any expected aud claim set up in the builder.
    • The iss claim matches the issuer the verifier is constructed with.
    • Any custom claim assertions that you add are confirmed
    $jwtVerifier = (new \Okta\JwtVerifier\JwtVerifierBuilder())
    ->setAdaptor(new \Okta\JwtVerifier\Adaptors\FirebasePhpJwt)
    ->setAudience('api://default')
    ->setClientId('${clientId}')
    ->setIssuer('https://${yourOktaDomain}/oauth2/default')
    ->build();

$jwt = $jwtVerifier->verify($jwt);

    Validating A Token Remotely With Okta

    Alternatively, you can also validate an access or refresh Token using the Token Introspection endpoint: Introspection Request. This endpoint takes your token as a URL query parameter and returns back a simple JSON response with a boolean active property.

    This incurs a network request which is slower to do verification, but can be used when you want to guarantee that the access token hasn't been revoked.

    See also

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